The invention relates to a device on a carding machine for setting the working gap between the cylinder and at least one neighbouring roller, which cooperate with one another with a small gap between their cylindrical surfaces (working gap) at the fibre transfer points.
The working gap may be readjustable to a pre-determined value as a result of changes in dimensions caused by thermal expansion and/or centrifugal forces. In carding, increasingly large amounts of fibre material are processed per unit of time, which requires higher working component speeds and higher performance. The increasing throughput of fibre material (production rate), even when the working surface area remains constant, results in increased generation of heat as a result of the mechanical work. At the same time, however, the technological carding result (sliver uniformity, degree of cleaning, nep reduction etc.) is constantly being improved, which requires a greater number of effective surfaces in carding engagement and narrower settings of those effective surfaces, e.g. fixed card tops and/or revolving card tops, with respect to the cylinder (tambour). The proportion of synthetic fibres being processed, which—compared with cotton—generate more heat as a result of friction when in contact with the effective surfaces (clothings) of the machine, is continually increasing. The working components of high performance carding machines are nowadays totally enclosed on all sides in order to conform to the high safety standards, to prevent the emission of particles into the spinning room environment and to minimise the need for servicing of the machines. Grids or even open, material-guiding surfaces allowing exchange of air are largely a thing of the past. The said circumstances markedly increase the input of heat into the machine, while the discharge of heat by means of convection is markedly reduced. The resulting more intense heating of high performance carding machines leads to greater thermo-elastic deformation which, on account of the non-uniform distribution of the temperature field, affects the set spacings of the effective surfaces: the gaps between cylinder and card top, doffer, fixed card tops and separation points are reduced. In an extreme case, the set gap between the effective surfaces can be completely consumed by thermal expansion, so that components moving relative to one another collide, resulting in considerable damage to the affected high performance carding machine. Accordingly, particularly the generation of heat in the working region of the carding machine can lead to different degrees of thermal expansion when the temperature differences between the components are too great.
Carding gaps and roller spacings on a carding machine are extraordinarily important. The carding quality stands or falls with the exact setting of those gaps (roller gaps). Under the action of heat, the rollers expand and the gaps change. In addition to expansion of the rollers caused by centrifugal force, which greatly changes the gaps, a high production rate and carding-intensive synthetic fibres additionally give rise to intense heating of the rollers. Thermally induced changes in the dimensions of the rollers occur. In order to achieve optimum carding quality it is necessary for the roller spacings to remain constant during operation. “Constant” means in this context that the change in spacing should be preferably less than 0.01 mm.
In a known device (DE 29 48 825), in a carding machine having at least two cooperating rollers the gap between the two rollers is changed in order to compensate for heating. This change is effected by means of additional mechanical displacement elements which are so constructed that they are able to change the spacing of the axes of the rollers in accordance with the prevailing temperature. For that purpose, the stationary framework of the carding machine is in the form of a frame having four supports (only two are shown) and having two horizontal longitudinal bars (only one is shown). The two longitudinal bars and the supports are joined together by crossbars (not shown) to form a stable, rigid support frame for two rotating rollers (cylinder and doffer) which are equipped with pointed clothing and operate a short distance a apart. The cylinder is fixedly mounted so as to be rotatable about its axis by means of two bearings (of which only one is shown) which are tightly screwed to the longitudinal bars by means of screws, and is driven and rotated. The doffer is likewise mounted so as to be rotatable about its axis by means of two bearings (only one is shown) on the longitudinal bars of the framework. The bearings for the doffer are not, however, tightly screwed to longitudinal bars but are each guided by means of two collar screws so that they are displaceable parallel to the axis by a small amount of the order of 1 to 2 mm. For that purpose, slot openings are provided in the bearings for the projecting screws, which allow exact lateral guidance of the bearings while ensuring their displaceability in the longitudinal direction. By parallel displacement of the bearings in the slot openings, the gap between the cylindrical surfaces of the two rollers can be varied. For that purpose, the machinery framework is provided on each of its longitudinal bars with a fixed stop for adjusting devices (displacement elements) which are inserted between the fixed stop and the bearing of the doffer. The adjusting devices are capable of determining the position of their corresponding bearing in respect of that of the fixed bearing for the cylinder. A disadvantage of this device is the structural complexity. Additional separate mechanical adjusting elements are required for displacement. A particular shortcoming is that the bearings of the high-speed doffer are displaceably arranged. In addition to the apparatus-related expense for the displacement elements on the bearings, the fact that the bearing arrangement for the heavy doffer roller is not completely rigid is a particular disadvantage. Displacement of the doffer that is only very slightly unequal results in a non-uniform roller gap and can lead to the destruction of the machine. In the known device, in every case the bearings of the doffer have to be loosened for adjustment and then fixed again.
It is an aim of the invention to provide a device of the kind described at the beginning which avoids or mitigates the mentioned disadvantages, which has an especially simple structure and enables a predetermined spacing between neighbouring rollers to be set in a simple manner in the event of changes in the dimensions of the rollers.